1. Field of the Invention
This invention relates generally to telecommunications. More particularly, it relates to wireless messaging and wireless emergency services such as E911.
2. Background of the Related Art
9-1-1 is a phone number widely recognized in North America as an emergency phone number that is used to contact emergency dispatch personnel. Enhanced 9-1-1 (E9-1-1) is defined by an emergency call being selectively routed to an appropriate public service access point (PSAP), based on a special identifier (P-ANI, or “Pseudo Automatic Number Identifier”, also referred to as “ESxK”), and includes the transmission of callback number and location information when 9-1-1 is used. E9-1-1 may be implemented for landline, cellular or VolP networks. A Public Service Answering Point (PSAP) is a dispatch office that receives 9-1-1 calls from the public. A PSAP may be a local, fire or police department, an ambulance service or a regional office covering all services. As used herein, the term “PSAP” refers to either a public safety access point (PSAP), or to an Emergency Call Center (ECC), a VoIP term.
Regardless of the network type, a 9-1-1 service becomes E-9-1-1 when automatic number identification and automatic location information related to the call is provided to the 9-1-1 operator at the PSAP. A primary challenge results from the fact that calls may arrive at the PSAP without the caller's actual callback number or location information displayed at the emergency operator's terminal.
The result of an E911 call is a direct circuit connection between the requestor and the responder. 911 is further enhanced with the ability to deliver location information over a data channel in parallel to the emergency call. This data is typically staged in a database that is queried by the PSAP to determine location information.
FIG. 3 depicts an overview of conventional enhanced 9-1-1 (E9-1-1) voice call flow in currently deployed architecture.
In particular, as shown in FIG. 3, an emergency voice call is initiated at a mobile station or handset 102, delivered through a relevant radio tower and base station 104 to a Mobile Switching Center (MSC) 206. The emergency voice call is then held while call setup information is delivered to a location center 222. The location center 222 responds to the MSC 206 with appropriate call routing information, and triggers a request for precise location. The MSC 206 releases the call and routes it to the correct PSAP through a selective router 210 based on information provided from the location center 222. The location center 222 then stages a record in an automatic location information (ALI) database 214. When the precise location information is returned to the location center 222 from a position determining entity 226, this location coordinate information is compared to a coordinate routing database 224, and the matching address and call back information is then staged for retrieval by the ALI database 214.
The current 911 infrastructure was designed to route a voice emergency call to the local PSAP. Unfortunately, this requires that voice circuits be available to carry the emergency call. During times of regional crises, such as a hurricane, the local wireless infrastructure can become overloaded by call volume. This was experienced during the September 11th terrorist attacks during which voice telecommunications along the East Coast was subject to service failures.